Phase component of spearer propodus out layer of mantis shrimp

The spearer propodus consisted ofthree layers including epicuticle (outer layer), exocuticle (middle layer), and endo-cuticle (inner layer). The outer layer was composed of fluorapatite, which was treatedas permeability barrier to environment.

The compact middle layer and inner layerwere constituted of chitin-protein fibers, which exhibited the layered spiral structure.Under the in-situ tensile test environment, spearer propodus owned high mechanicalstrength, which bore maximum tensile fore of 320 N. In the in-situ tensile process,cracks extended along with zigzag lines on spearer propodus surface. The middlelayer and inner layer resisted the damage of force via the fracture and pulling offibers.